The retention of blade fragments from the rotors of turbine engines rotating at a high velocity has rendered the develpoment of devices for the removal of the blade or of the fragment without their damaging the rest of the blading, necessary. The devices known heretofore are intended either to retain the fragments resulting from the fracture, or to fragment them so that they may be removed without damage.
U.S. Pat. No. 3,241,813 describes a device for the retention of fragments of the rotor of a turbine. A ring made of a high strength material surrounds the rotor and supports an annular body consisting of a metal capable of resisting the impact of the fragments without the risk of failure. The annular body, facing the blades of the rotor, represents an annular conduit.
Part of the kinetic energy of the blade fragment or blade ejected is dissipated, during its impact, by the deformation or fracture of the annulus, and the rest of the energy by the friction of the annulus and the annular body in the casing wherein they are secured by shrinkage.
In a second form of embodiment described, the annular conduit is lined internally by a material that is softer than that of the annular conduit so as to permit its penetration by the fragments while expending their energy and their retention therein. The material selected is aluminum.
The above-described devices are effective but have the disadvantage of being rather heavy. In fact, the materials used for the annulus and the annular body are generally high strength steels with a relatively large thickness. The result is an appreciable increase in the weight of the aircraft. The replacement of steel by titanium, which has a lower specific gravity, reduces the weight but increases the cost of manufacture.
French Pat. No. 1,604,806 describes structures capable of resisting the projectiles and consisting of layers of a fibrous material and layers formed of pieces of a rigid materials having a diamond hardness higher than 700. These rigid pieces are rods or thick walled tubes, balls, natural gravel or pebbles. The density of the plates obtained in this manner is of the order of 2.5. The rigid pieces have the function not only of resisting the action of a projectile, but also of deflecting and inducing its fracturing into fragments.
The production of a retaining structure for the casing of a compressor based in the teaching of the latter patent has not been eased by its use of a very hard material. The assembly of these armor elements does not lend itself to the formation of cylindrical layers that would facilitate the displacement of the blade fragment or of the blade in the material and the progressive absorption of its kinetic energy.